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The TNM alloy, a βo-phase-containing TiAl alloy, has been withdrawn from use as a last-stage turbine blade in commercial jet engines as it suffered frequent impact fractures in service, raising doubts regarding the necessity of the βo-phase in practical TiAl alloys. Here, we evaluate the prac-tical properties required for jet engine blades for various TiAl alloys, and investigate the effects of the βo-phase thereupon. First, we explore the influence of the βo-phase content on the impact re-sistance and machinability for forged Ti–43.5Al–xCr and cast Ti–46.0Al–xCr alloys; the properties deteriorate significantly at increasing βo-phase contents. Subsequently, two practical TiAl al-loys—TNM alloy and TiAl4822—were prepared with and without the βo-phase by varying the heat treatment temperature for the former and the Cr concentration for the latter. In addition to impact resistance and machinability the creep strength is significantly reduced by the presence of the βo-phase. Overall, these findings suggest that the βo-phase is an undesirable phase in practical TiAl alloys, especially those used for jet engine blades, because, although the disordered β-phase is soft at high temperatures, it changes to significantly more brittle and harder βo-phase after cooling.

Rights:

• Creative Commons BY Attribution 4.0 International
  

Keyword: titanium aluminides, impact resistance, machinability, creep strength, jet engine blades

Date published: 2024-08-09

Publisher: MDPI AG

Journal:

• Metals (ISSN: 20754701) vol. 14 issue. 8 908

Funding:

• Japan Science and Technology Agency AS0216001

Manuscript type: Publisher's version (Version of record)

MDR DOI:

First published URL: https://doi.org/10.3390/met14080908

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Updated at: 2024-08-30 16:30:54 +0900

Published on MDR: 2024-08-30 16:30:54 +0900